Conventionally, there are games, such as action games and roll-playing games, in which a player character moves in a virtual three-dimensional game space in accordance with an operation of a user. Generally, the three-dimensional game space is generated by computer graphics. In recent years, the computer graphics has high definition and can express actual scenery and the like with a high degree of reproduction. However, such expression by the computer graphics is not equal to an actual video image (real video image) taken by a video camera or the like.
Games have been developed, in which characters can be operated in the three-dimensional game space generated by using actual video images instead of background images generated by computer graphics (see Non Patent Literature 1, for example).